For some applications, it is desirable to produce an optical-quality, parabolic optical surface on a lateral surface of a light-transmissive solid body. A light beam directed through the light-transmissive solid body parallel to the parabolic axis and toward the parabolic surface is reflected from the parabolic surface to pass through the parabolic focus. Similarly, a light beam originating at the parabolic focus reflects from the parabolic surface and travels parallel to the parabolic axis. For example, a glass (for visible light) or silicon (for infrared light) solid-body optical element having its lateral surface formed to the parabolic shape may be required for various types of optical applications.
The fabrication of a parabolic lateral surface on a light-transparent body is typically performed by a combination of grinding and polishing the lateral surface of the light-transparent body. The shape of the lateral surface must be carefully measured as the grinding and polishing proceeds, to ensure that the final lateral surface will have the required precisely parabolic shape. Thus, during the grinding-and-polishing operation the shape of the surface may be periodically checked by mechanical inspection techniques to be certain that it is converging on the desired parabolic shape. The grinding-and-polishing procedure is altered and fine-tuned as a result of the measurements, to achieve the desired final parabolic shape.
While this approach is operable to some extent, it has drawbacks. The mechanical inspection procedure is cumbersome and difficult to perform without removing the light-transparent body from the grinding-and-polishing apparatus. The degree of precision required may also be greater than can readily be determined by mechanical measurements. As the lateral surface approaches its final shape, achieving a precisely curved surface is therefore difficult.
There is a need for an improved approach to the fabrication of a parabolic optical lateral surface on a light-transparent body. The present invention fulfills this need, and further provides related advantages.